The French conquest of Vietnam (1858–1885) was a long and limited war fought between the Second French Empire, later the French Third Republic and the Vietnamese empire of Đại Nam in the mid-late 19th century. Its end and results were victories for the French as they defeated the Vietnamese and their Chinese allies in 1885, the incorporation of Vietnam, Laos, and Cambodia, and finally established French rules over constituent territories of French Indochina over Mainland Southeast Asia in 1887.

A joint Franco-Spanish expedition attacked Da Nang in 1858 and then retreated to invade Saigon. King Tu Duc signed a treaty in June 1862 granting the French sovereignty over three provinces in the South. The French annexed the three southwestern provinces in 1867 to form Cochinchina. Having consolidated their power in Cochinchina, the French conquered the rest of Vietnam through a series of battles in Tonkin, between 1873 and 1886. Tonkin at that time was in a state of near anarchy, descending into chaos; both China and France considered this area to be their sphere of influence and sent troops there.

The French eventually drove most of the Chinese troops out of Vietnam, but a remnant of its armies in some Vietnamese provinces continued to threaten French control of Tonkin. The French government sent Fournier to Tianjin to negotiate the Tianjin Accord, according to which China recognized the French authority over Annam and Tonkin, abandoning its claims to suzerainty over Vietnam. On June 6, 1884, Treaty of Huế was signed, dividing Vietnam into three regions: Tonkin, Annam, and Cochinchina, each under three different separate regimes. Cochinchina was a French colony, while Tonkin and Annam were protectorates, and the Nguyễn court was put under French supervision.